U.S. patent number 4,350,528 [Application Number 06/158,761] was granted by the patent office on 1982-09-21 for method for diffusion bonding workpieces and article fabricated by same.
This patent grant is currently assigned to TRW Inc.. Invention is credited to Edgar W. Engle.
United States Patent |
4,350,528 |
Engle |
September 21, 1982 |
Method for diffusion bonding workpieces and article fabricated by
same
Abstract
A diffusion bonding method for assembling members formed from a
liquid phase system material into a monolythic structure free of
flaws and distortion. Member blanks are first formed from the
material as by compacting or the like and then sintered to have
their full density and hardness characteristics. Following
sintering, any special surface or internal features are machined
into the blanks to define the members. The members are also
provided with bonding surfaces adapted to be placed in mating
engagement with each other. The members are placed in an assembled
relationship with the bonding surfaces engaging each other to
define a bonding zone. In some cases, it may also be desirable to
place a weight on the assembled members to continuously urge the
bonding surfaces toward engagement. In the actual bonding step, the
members are heated in a vacuum environment to a temperature
intermediate the melting temperatures of the material low and high
melting phase components. During such heating, the liquid phase
system material of the two members coalesce across the boundary
zone to effect an integral joint or bond.
Inventors: |
Engle; Edgar W. (Rogers,
AR) |
Assignee: |
TRW Inc. (Cleveland,
OH)
|
Family
ID: |
22569591 |
Appl.
No.: |
06/158,761 |
Filed: |
June 12, 1980 |
Current U.S.
Class: |
419/8; 228/174;
228/193 |
Current CPC
Class: |
B22F
7/062 (20130101) |
Current International
Class: |
B22F
7/06 (20060101); B22F 007/02 () |
Field of
Search: |
;75/28R,203,204
;428/565 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Allan
Attorney, Agent or Firm: Blackhurst; Daniel G.
Claims
Having thus described the invention, it is now claimed:
1. A method for diffusion bonding at least a pair of bodies to each
other at a bond zone defined at the interface of cooperating
surfaces of said bodies disposed in a contacting relationship with
each other and wherein each of said bodies is formed of a cemented
tungsten carbide material which includes cobalt as a low melting
phase component and tungsten carbide as a high melting phase
component, said method comprising the steps of:
sintering each of said bodies in an inert atmosphere to a
temperature intermediate the melting temperature of said low and
high melting phase components thereof to obtain substantially the
full density and hardness characteristics for said bodies;
shaping said bodies to have substantially the desired conformations
with one of said bodies having a first bond surface and the other
of said bodies having a second bond surface, said first and second
bond surfaces adapted to substantially mate with each other;
placing said first and second bodies in an assembled relationship
with each other so that said first and second bond surfaces are in
engagement and define said bond zone; and,
heating said bodies in said assembled condition in an inert
atmosphere to a temperature intermediate the melting temperatures
of the low and high melting phase components thereof for causing
grains in said first and second bodies at least adjacent said first
and second bond surfaces to grow across said bond zone and thereby
effect an integral interconnection between said bodies.
2. The method as defined in claim 1 further including the step of
applying pressure to said bodies at least during said step of
heating for continuously urging said first and second bond surfaces
toward close mating engagement with each other.
3. The method as defined in claim 1 further including the step of
treating at least one exposed surface of said assembled bodies to
have a desired surface finish following said step of heating.
4. A method for joining at least a pair of members compacted from
cemented carbide materials which include cobalt as a low melting
phase component and tungsten carbide as a high melting phase
component and wherein each member has been sintered in order to
substantially obtain the full density of hardness characteristics
thereof, said method comprising the steps of:
preparing a first joining surface on one of said members and a
second joining surface on the other of said members so that said
first and second joining surfaces are adapted to substantially mate
with each other;
positioning said members in an assembled relationship with each
other with a first joining surface of one member in engagement with
a second joining surface of the other member for defining a
boundary zone; and,
heating said members in said assembled relationship in an inert
atmosphere to a temperature intermediate the melting temperatures
of said low and high melting phase components for causing
coalescence of said members across said boundary zone and effecting
integral interconnection between said members.
5. The method as defined in claim 4 further including the step of
applying pressure to said members at least during said step of
heating for continuously urging said first and second joining
surfaces toward close mating engagement with each other.
6. The method as defined in claim 4 further including the step of
preparing at least said first and second joining surfaces prior to
said step of positioning so that said joining surfaces will closely
mate with each other in said assembled relationship.
7. The method as defined in claim 6 including machining any desired
conformation into said members during said step of preparing.
8. A method for bonding at least a pair of components to each other
at some predetermined boundary therebetween so that said components
become substantially integral with each other wherein said
components are each formed from a cemented carbide material which
has been compressed into some predetermined configuration and
thereafter sintering to substantially obtain the full density and
strength characteristics thereof, said method comprising the steps
of:
shaping said components to generally have the final desired
conformation therefor with one of said components having a first
bonding surface and the other of said components having a second
bonding surface, said first and second bonding surfaces being
finished to accommodate selective placement thereof in a close
mating relationship with each other;
placing said components in an assembled condition wherein said
first and second bonding surfaces closely matingly engage and
define said boundary; and,
heating said components in said assembled condition in an inert
atmosphere to a temperature within the range of sintering
temperatures for said cemented carbide material for causing grains
in each of said components adjacent said first and second bonding
surfaces to grow across said boundary and effect an integral
component interconnection.
9. The method as defined in claim 8 further including the step of
applying pressure to said components at least during said step of
heating for continously urging said first and second bonding
surfaces toward close mating engagement with each other.
10. The method as defined in claim 8 wherein said step of shaping
further includes locating at least one of said components on a mold
surface having some predetermined desired conformation, causing at
least said one component to be heated to a temperature within the
range of its sintering temperatures to effect softening thereof and
allowing said one component to assume the conformation of said mold
surface.
11. The method as defined in claim 8 wherein said cemented carbide
material comprises tungsten carbide and at least said heating step
is performed at a temperature generally in the range of
1380.degree. C.-1480.degree. C. in a vacuum environment of less
than 750 microns at said temperature.
12. The method as defined in claim 11 further including the step of
positioning a weight on said components in said assembled condition
for continuously urging said first and second bonding surfaces
toward close mating engagement during said step of heating, said
weight generally being less than 480 gms./in.sup.2 of surface area
at said boundary.
Description
BACKGROUND OF THE INVENTION
This application pertains to the art of bonding or joining and more
particularly to integrally bonding at least a pair of workpieces to
each other.
The invention is particularly applicable to use with workpieces
formed from a liquid phase system material such as cemented
carbide, including cemented tungsten carbide and the like, and will
be described with particular reference thereto. However, it will be
appreciated that the invention has far broader applications and is
deemed equally applicable to other types of liquid phase system
materials.
Cemented carbide materials are formed into various shapes and
configurations by techniques associated with the art of powder
metallurgy. These techniques are well known and generally involve
the process of consolidating metal powders into ingots or shaped
parts without fusion or at least without fusion in the major
portion of the powder components. Typically, the procedure involves
pressing or compacting the powder into some desired shape and then
heating or sintering the compact at a temperature below the melting
point of its highest melting point constituent. It is known that
cemented carbide pieces or members will stick to each other if
placed in contact during the sintering operation.
It is often desired to fixedly interconnect a plurality of sintered
carbide components to each other so as to define a subassembly or
some finished article. Heretofore, such interconnections have been
accomplished by several means including brazing and bonding under
elevated temperature-pressure conditions. In such bonding, the
temperature involved is approximately the same as that for
sintering and the pressure is approximately in the range of 1000
psi or so. However, the resultant bonds were not entirely
satisfactory and the process itself did not accommodate joining
members which included intricate designs such as ducts, passages,
grooves and the like.
One particular situation where the foregoing problems are apparent
is in the manufacture of optical elements or mirrors which are
utilized for high energy laser applications. The performance of
high energy lasers is greatly influenced by the configuration of
the optical elements involved. Small distortions of the optical
surfaces may severely degrade the laser beam coherence and
therefore, reduce its effectiveness. The mirrors themselves
generally involve a configuration comprised of a plurality of
components including a mirror surface or faceplate and a heat
exchanger. These components include intricate configurations and/or
relationships and must be fixedly secured to each other in the
final mirror structure.
At the present time, mirrors and other optical elements for high
energy laser applications are conventionally made from molybdenum.
Such constructions are, however, approaching their limit of low
distortion under high laser beam power density. Accordingly, it has
been proposed to construct such mirrors from cemented tungsten
carbide since it has about the same thermal conductivity as
molybdenum, a lower coefficient of thermal expansion and a much
higher modulus of elasticity. As a result, tungsten carbide is
considered to be inherently better for low distortion mirror
applications than molybdenum. However, to successfully manufacture
or fabricate mirrors from the material adapted for laser
applications, it has been necessary to develop a process or system
whereby the various mirror components could be assembled into a
monolythic structure free of flaws and distortion. The method or
system should also readily accommodate joining components which
include intricate designs without in any way damaging or impairing
the designs during bonding or joining.
The subject invention provides a method or system which meets the
foregoing needs and overcomes problems encountered with prior known
bonding techniques employed for fixedly securing cemented carbide
members to each other. In addition, and while application of the
invention will hereinafter be specifically described with reference
to a cemented tungsten carbide mirror construction, the invention
is deemed broadly and equally applicable to joining or bonding
other types of components or members formed from various liquid
phase system materials adapted to use in other applications and/or
environments.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the present invention, there is provided a
method of diffusion bonding or joining at least a pair of members
which are compacted from liquid phase system materials which
include low melting phase components and high melting phase
components and wherein each member has been sintered for obtaining
substantially the full density and hardness thereof. The method
involves the step of placing the members in an assembled
relationship with a first bonding or joining surface on one of the
members in mating engagement with a second bonding or joining
surface on the other of the members to define a bonding or boundary
zone. Thereafter, the step of heating the members in the assembled
relationship is employed. This heating is to a temperature
intermediate the melting temperatures of the low and high melting
phase components of the members for coalescence of the members
across the bonding zone and to effect an integral interconnection
therebetween. In other words, the heating step causes a grain
growth between the two members across the bonding zone at least
adjacent the first and second bonding surfaces.
According to another aspect of the method, a separate step of
preparing the first and second bonding surfaces is included. This
step assures mating engagement between the surfaces when the
members are placed in their assembled relationship.
In accordance with yet another aspect, the method includes the step
of applying a pressure to the members at least during the step of
heating for continuously urging the first and second bonding
surfaces into close mating engagement with each other. For some
bonding surface configurations and finishes, applying pressure will
enhance the diffusion bond across the bonding zone.
The step of preparing further includes shaping or machining any
desired special or intricate conformations or designs into the
members themselves. Such shaping or machining is performed
subsequent to sintering and prior to the step of heating.
The preferred application of the method is to members or components
formed from cemented carbide materials and, more particularly, from
cemented tungsten carbide.
In accordance with still a further aspect of the invention, an
article or workpiece is provided and advantageously formed from
liquid phase system material which includes low melting phase
components and high melting phase components. The article includes
at least a pair of article members which have been compressed from
articles of the system material and sintered to generally have
their full density and hardness characteristics. A bonding surface
is included on each of the article members and configured to
substantially mate with each other for defining a boundary zone
when the members are placed in their desired assembled
relationship. An integral interconnection between the members is
provided across the boundary zone. This interconnection is effected
by heating the components in their assembled relationship to a
temperature intermediate the melting temperatures of the system low
and high melting phase components. Such heating causes a
coalescence or grain growth between the two members across the
boundary zone at least adjacent the mounting surfaces.
The principal object of the present invention is the provision of a
new method for diffusion bonding or joining members or workpieces
and an article fabricated by the method.
Another object of the invention is the provision of such a method
and article in which distortion of the component members is
eliminated or at least substantially reduced at an area of
interconnection therebetween.
Anther object of the invention is the provision of a new bonding
method and article which may be readily adapted to use with a wide
variety of different liquid phase system materials and for a wide
variety of member or article configurations used in any number of
different environments.
Still other objects and advantages for the invention will become
apparent to those skilled in the art upon a reading and
understanding of the following specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take physical form in certain parts and
arrangements of parts, preferred and alternative embodiments of
which will be described in detail in this specification and
illustrated in the accompanying drawings which form a part hereof
and wherein:
FIG. 1 is a generally schematic side elevational view of a laser
mirror formed in accordance with the present invention;
FIG. 2 is an exploded view of the mirror components in their rough
formed condition subsequent to sintering;
FIG. 3 is a view similar to FIG. 2 showing the components following
sizing and shaping thereof prior to application of the subject new
bonding process;
FIG. 4 is a block diagram generally showing the steps contemplated
in practicing the subject new method;
FIG. 5 is a generally perspective view which sequentially shows the
steps involved in forming one type of heat exchanger for a laser
mirror utilizing the concepts of the subject invention;
FIG. 6 is an exploded perspective view showing the basic mirror
components which incorporate the heat exchanger arrangement of FIG.
5 and which mirror is assembled using the concepts of the subject
invention; and,
FIG. 7 is a generally schematic view which sequentially shows the
steps for obtaining some predetermined curvature in the mirror heat
exchanger and faceplate.
DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE
EMBODIMENTS
Referring now to the drawings wherein the showings are for purposes
of illustrating preferred and alternative arrangements of the
invention only and not for purposes of limiting same, FIG. 1 shows
a mirror construction A particularly suited for high energy laser
applications and which mirror has been formed and/or assembled in
accordance with the concepts of the present invention. While the
invention will be described in detail with reference to such mirror
as well as variations thereof, it will be readily appreciated by
those skilled in the art that the invention has broader
applications and may be utilized for integrally joining any number
of separate components to each other for a wide variety of uses or
applications. Moreover, and while the mirror construction will be
specifically described with reference to cemented tungsten carbide,
it will also be appreciated that the invention is fully applicable
to use with other cemented carbide materials as well as in other
types of liquid phase systems.
More particularly, mirror A is comprised of three basis sections
which are integrally joined with each other pursuant to the new
bonding method. These sections comprise faceplate 10, a heat
exchanger 12 and a substrate or base 14 which are compatible with
each other and which may have generally circular, rectangular or
square configurations. Faceplate 10 includes a planar outer or
mirror surface 20 with a planar inner surface 22. Heat exchanger 12
includes spaced apart parallel upper and lower planar surfaces
24,26. Upper surface 24 includes a plurality of spaced apart
coolant flow channels 28 therein which are advantageously employed
to acommodate coolant flow therethrough at least during high energy
laser applications. Substrate or base 14 includes spaced apart
parallel upper and lower planar surfaces 30,32. The substrate or
base may conveniently and advantageously include internal passages
or the like to reduce the substrate weight and/or to facilitate
flow communication with heat exchanger coolant flow channels 28.
One such passage is schematically shown in FIG. 1 and designated by
numeral 34. Insofar as the details of the subject invention are
concerned, faceplate 10, heat exchanger 12 and substrate or base 14
are integrally interconnected at surfaces 22,24 and surfaces 26,30
which define bond or boundary zones a,b, respectively.
Referring more particularly to FIGS. 2, 3 and 4, description will
hereinafter be made to the detals of the mirror construction of
FIG. 1, including the specifics of the diffusion bonding or joining
process. In FIG. 4, the first step is designated by numeral 50 and
comprises preparing rough blanks for ultimate processing into the
faceplate, heat exchanger and substrate components described above.
These blanks may be individually prepared by compacting tungsten
carbide powder mixed with cobalt powder. Specifically, the mirror
described above has been constructed from two different grades of
cemented tungsten carbide, namely one having 6% cobalt and another
having 9% cobalt. In processing cemented tungsten carbide to form
blanks for the mirror components, conventional powder metallurgy
techniques are employed wherein the tungsten carbide powder
comprises a high melting phase component and the cobalt comprises a
low melting phase component. Since such processing techniques are
well known in the art, a detailed discussion thereof has not been
included. An acceptable alternative to individually preparing the
rough blanks is to press or compact the cemented tungsten carbide
material into a billet and then rough cut or saw the individual
mirror components therefrom. This alternative is shown in FIG. 4
and designated by numeral 52.
The blanks are then sintered as indicated by method step 54 in FIG.
4. Such sintering is performed in a vacuum oven or furnace to
obtain substantially the full blank density and hardness and with
the blanks arranged in a non-contacting relationship with each
other. During sintering, and for the specific cemented tungsten
carbide materials which have been utilized for the mirror
construction, a linear shrinkage of approximately 17% or so for
each blank will be involved. The sintering temperature and vacuum
conditions utilized are conventional for the particular material
employed. Following sintering, the blanks which comprise faceplate
10, heat exchanger 12 and substrate 14 will have the general
configurations shown in FIG. 2.
Because the overall mirror construction requires certain intricate
structural conformations in the individual components, it is
necessary to next size and shape the blanks as indicated by step 56
in FIG. 4. Such sizing and shaping is typically accomplished by
grinding or other appropriate material removal operations and will,
with reference to FIG. 3, include formation of coolant flow
channels 28 in heat exchanger upper surface 24 and the necessary
and desirable passages or channels 34 in substrate or base 14. In
addition, it is desirable that inner and upper surfaces 22,24 and
lower and upper surfaces 26,30 be machined in a manner so that they
will substantially matingly cooperate for defining bond zones a,b
(FIG. 1) when the mirror components are placed in an assembled
relationship. A precise mating relationship is preferred since the
joining process involves grain growth or coalescence across the
bonding zones as will become more readily apparent hereinafter.
The sizing and/or shaping steps required for the blanks as
indicated by numeral 56 in FIG. 4 are a function of the particular
workpiece and blanks involved and the particular physical and/or
dimensional characteristics required therefor in order to
satisfactorily meet an intended use. Thus, for some members or
components which are carefully prepared in the blank stage, no
sizing and/or shaping steps may be required.
The components are next cleaned, assembled and placed in a vacuum
oven or furnace for diffusion bonding in accordance with the
process of the invention. This step is indicated by numeral 58 in
FIG. 4. In the case of laser mirror A, such assembly merely
comprises stacking the components relative to each other in their
final desired relationship with surfaces 22,24 and surfaces 26,30
in engagement with each other to define bonding zones a,b.
Depending on the precise nature of the mating relationship between
these cooperating surfaces, it may be desirable to slightly weight
the assembled components for continuously urging surfaces 22,24 and
surfaces 26,30 into enagement.
For the particular cemented tungsten carbide materials used in
fabricating laser mirror A of FIG. 1, the carbide block or the like
is employed and simply placed on outer surface 20 of faceplate 10.
While the specific weight desired will vary as a function of the
surface finish and mating relationship between the cooperating
surfaces, a normal weight or unit pressure in the range of 0-480
gms/in.sup.2 of bonding zone area at either of zones a,b is
typically employed for laser mirror A. However, improvement of the
mating relationship between surfaces 22,24 and surfaces 26,30
allows this weight or unit pressure to be substantially reduced or
even entirely eliminated.
As previously noted, cooperating surfaces 22,24 and 26,30 define
bonding zones or boundaries a,b. In accordance with the present
invention, faceplate 10, heat exchanger 12 and substrate or base 14
are diffusion bonded together at these bond zones as indicated by
the method step 62 in FIG. 4. This diffusion bonding is achieved by
heating the assembled components in a vacuum furnace to a
temperature generally in the range of the sintering temperature,
i.e., intermediate the melting tempertures of the material low and
high melting phase components. It has been found that for laser
mirror A fabricated from cemented tungsten carbide having 6% or 9%
cobalt, a diffusion bonding temperature in the range of
1380.degree. C.-1480.degree. C. is particularly preferred. Such
temperatures are above the melting temperature for the low melting
phase component of cobalt, i.e., 1300.degree. C. for fine grain
sizes, and below the temperature where there is massive melting,
i.e., approximately 1490.degree. C. It is also considered desirable
to perform the bonding process at a temperature which is more
closely spaced toward the lower range of melting temperatures for
the low melting phase component.
In addition, the diffusion bonding is preferably performed in a
vacuum environment. While the precise vacuum condition may vary
somewhat as a function of the heating furnace capabilities, a
vacuum of less than 750 microns at the bonding temperature is
desired for the particular mirror construction involved. A vacuum
in the range of approximately 200 microns or so is generally
preferred. Here also, these parameters may be varied somewhat as
deemed necessary and/or appropriate to suit a particular bonding
situation or application. For example, a controlled hydrogen
atmosphere environment may be satisfactorily employed.
During heating to secure diffusion bonding, grains in faceplate 10
and heat exchanger 12 at least adjacent surfaces 22,24 thereof and
grains in heat exchanger 12 and substrate 14 at surfaces 26,30
thereof grow across the bonding zones a,b (FIG. 1) defined thereby.
Thus, there is complete coalescence of the faceplate, heat
exchanger and substrate components at least across their
cooperating bonding zones or boundaries so that the components
thereof are joined or bonded in an integral relationship. Indeed,
photomicrographs of a cross-section in a laser mirror A following
diffusion bonding reveals that such grain growth or coalescence is
so complete that it is virtually impossible to determine where the
original bond zones or boundaries were defined between the
individual components. Since the individual component blanks are
sintered prior to the diffusion bonding step for obtaining full
density and hardness in the blanks, there is no further shrinkage
or distortion in the resultant components at the time of bonding.
This result is extremely advantageous for the laser mirror
application in that any distortion may severely degrade laser beam
coherence and reduce its effectiveness when the mirror is placed
into use.
Following diffusion bonding, any final part treatments may be
performed as indicated by the step designated 64 in FIG. 4. In the
case of the laser mirror, such final treatments would include
polishing faceplate outer or mirror surface 20 (FIG. 1) to obtain
the necessary optical characteristics. In the event the faceplate
has any defects and cannot be polished to the desired finish, it
may be coated by chemical vapor deposition using known techniques
of a thin layer of pure tungsten which has good polishing
properties. Of course, other final treatment steps may be required
and/or desired for other types of components, parts and the like
formed from other liquid phase system materials and bonded together
in accordance with the diffusion bonding process of the subject
invention.
FIG. 5 schematically shows the sequence of steps involved in
forming a subassembly using the subject invention and wherein the
subassembly is to later become a part of a larger assembly or
article. In FIG. 5, step A shows a heat exchanger blank 70 which
has already been sintered and includes a planar upper surface 72.
In step B a plurality of coolant flow channels 74 are ground or
otherwise machined into upper surface 72 so as to be disposed in a
side by side generally parallel relationship with each other.
Thereafter, in step C, a second blank 76 which has been previously
sintered and prepared is placed on top of blank 70 so as to cover
upper surface 72 and provide a top surface for coolant flow
channels 74. Blanks 70,76 are diffusion bonded to each other in the
manner hereinabove described with reference to FIG. 4. Following
joining, step D shows a final treatment step wherein a plurality of
coolant flow channels 78 are ground in second blank upper surface
80 in a parallel spaced apart relationship. The structure shown in
step D thus comprises a double pass heat exchanger subassembly
82.
FIG. 6 shows an exploded perspective view of the circular laser
mirror construction which includes heat exchanger 82 as a
subassembly thereof. More particularly, the mirror shown includes a
face plate 90, heat exchanger 82, a heat exchanger frame 94 and a
substrate or base 96. Frame 94 includes a square center opening 98
adapted to receive and provide support for heat exchanger 82 while
accommodating coolant flow through the heat exchanger. Substrate 96
includes side wall passages or the like with one such passage
generally designated 100. At least some of these passages
appropriately communicate with inlet and outlet manifolds 102,104
which, in turn, communicate with the heat exchanger in the final
mirror assembly.
In assembling the mirror construction of FIG. 6, heat exchanger
assembly 82 and frame 94 may first be bonded together utilizing the
diffusion bonding concepts of the subject invention so that the
heat exchanger is retained within frame opening 98. Thereafter,
face plate 90, heat exchanger 82 with frame 94 and substrate 96 may
be advantageously diffusion bonded together. The arrangement of
FIG. 6 demonstrates the versatility of the subject new bonding
method for use in joining subassembly components and for then
joining the subassembly components into a final article.
Finally, FIG. 7 sequentially demonstrates further versatility in
using the subject bonding method as demonstrated in obtaining a
concave or convex mirror construction. For ease of illustration,
like components are identified by like numerals with a primed (')
suffix and new components are identified by new numerals.
To obtain heat exchanger and face plate concavity, flat face plate
90', heat exchanger 82' and frame 94' are diffusion bonded together
as previously described. In step A of FIG. 7, the subassembly is
located on a die 110 which has a die surface 114 of a desired
spherical curvature. For the particular cemented tungsten carbide
material employed for the laser mirrors described herein, the die
is constructed from graphite.
The die and mirror components are then heated to the sintering
temperature of the components and at this temperature, face plate
90', heat exchanger 82' and frame 94' become soft enough to sag
into the graphite mold under the influence of gravity alone. As
shown in part B of FIG. 7, such sagging causes outer or mirror
surface 114 of faceplate 90' to assume a concave conformation
substantially similar to that of die surface 112. Since the
individual components have been previously sintered to
substantially their full density and hardness and then diffusion
bonded together, the step of reheating to obtain curvature does not
in any way cause distortion in the components involved.
Finally, step C of FIG. 7 shows this subassembly after bottom
surface 116 thereof has been conveniently ground or machined to a
flat condition. Likewise, peripheral side edge 118 is machined or
otherwise processed to be generally normal to bottom surface 116.
Thereafter, the subassembly may be conveniently bonded to an
associated substrate using those diffusion bonding techniques
hereinabove previously described.
While the invention has been specifically described with reference
to fabricating a laser mirror from a cemented tungsten carbide, it
should be readily appreciated by those skilled in the art that the
new diffusion bonding system has far broader applications and may
be used in bonding any number of different types and configurations
of components to each other to define a completed workpiece or part
or some subassembly therefor. Moreover, it will also be appreciated
that the type of material involved is not limited to cemented
tungsten carbide but indeed, it is considered to be applicable to
many types of liquid phase systems which include low melting phase
components and high melting phase components. The specific
operational parameters for the bonding process necessarily vary as
between such materials, but generally fall in the range of those
utilized for sintering such materials.
The invention has been described with reference to preferred and
alternative embodiments. Obviously, modifications and alterations
will occur to others upon the reading and understanding of this
specification. It is intended to include all such modifications and
alterations insofar as they come within the scope of the appended
claims or the equivalents thereof.
* * * * *